Traffic signal control



Dec. 22 1936; H. B. BRAINERD TRAFFIC SIGNAL CONTROL Filed May 21, 1931 3 Sheets-Sheet l (3 INVFNTOR. BY WK M.

A TTORNE Y.

Dec. 22, 1936. H. B. BRAINERD TRAFFIC SIGNAL CONTROL Filed May 21, 1931 3 Sheets-Sheet 2 l N VEN TOR.

A TTORNE Y.

Sheets-Sheet 3 Dec 22, 1936 H. B. BRAINERD TRAFFIC SIGNAL CONTROL Filed May 21, 1951 4 t5 as {3 INVELNTOR.

BY W K ATTORNEY.

, Patented Dec. 22, loss j UNITED STATES PATENT OFFICE mamc SIGNAL ooN'moL I Henry B. Brainerd, Wellecley, Application May 21', 1931, Serial No. 539,011 a Claims. (-01. iii-33a The present invention relates toa system for automatically detecting the presence and controlling the operation of free vehicles, by which is intended land vehicles operated on a highway, 5 and characterized by their normal independence from any track or similar close limitation of their path of travel and by capacity for being steered, such vehicles comprising the usual automotive highway traflic.

Systems for automatically controlling the flow o1 traflic across intersecting lanes of travel have heretofore so far as I am aware employed a timed delay principle, the time interval being predetermined and largely inflexible, so that the trailic has to wait on the signal and accommodate itself thereto, instead of the signal being responsive to the trafiic. In recognition of this fundamental drawback, attempts have been made to cause the signals to be worked with some regard to the actual instead of the presumptive conditions of trafilc, and to this end resort has commonly been had to a vehicle detector located at 'a point considerably removed from an intersection. The detector is effective to operate a signal or other traific control device whenever a vehicle passes the point where it is located. A timed delay device serves to hold the signal in operated position for a length of time assumed to be required tor the vehicle to pass from the point of location of the detector to the margin of the intersection and for sufficient additional timefor the vehicle to have presumably passed the-intersection. The time periods must necessarily be liberal to accommodate slow moving vehicles and obviously result in many unnecessary delays to crossing trafllc.

The limitation of. such systems is that they detect the presence of vehicles only at a point, or at best at two points in the neighborhood of 40 the approach to the intersection, and because they have no way of. detecting the subsequent action of the vehicle after passing the single detector, or the first detector of a pair at opposite ends of the approach, they must rely on a timed delay during which the vehicle or vehicles actuating the detector are presumed to have eflected a crossing. This presumption may just as easily be wrong as right, as is an unavoidable consequence. The attempt to avoid the timed delay through the use of two detectors acting each at a point introduces further problems, such as that of the vehicle which actuates the first detector and then through changing its course fails to actuate the second, which in turn require the provision of delicate and complicated compensating devices which are expensive and which also introduce the timed delay to correct the signaling. Furthermore the operation of such systems as are mentioned above may be disarranged by a vehicle whichleaves the intersectionover a lane normally used by approaching vehicles, such disarrangement continuing after its cause has departed.

The general object of the invention is to provide a novel and improved automatic traflic signal controlling system which shall be solely and completely responsive to the actual conditions and needs of traflic at all times even while these needs are frequently changed by the changes in volume, route, and direction of such trafilc, and which shall avoid the obvious defects of existing systems known to me.

A particular object of the present invention is to provide'an improved system using novel means for automatically controlling traflic, which shall obviate the use of the timed delay principle of operation, which is the basis of the common alternating timed signals and of the present detector'controlled timed signals, also. Another object of the invention is the provision of novel vehicle-actuated detector means for controlling the signals which shall not be subject to injury by the vehicles themselves or be subject to damage or interference with its operation through the action of water, ice, mud and gravel, or through intentional tampering. A further object of the invention is to provide a system and detector means therefor which will be directly and accurately responsive to the relative volumes of traflic on the intersecting highways andwill give precedence to conflicting trafiic in proper accordance with the fundamental principles of priority of approach to the intersection. A further object of the invention is the avoidance in such organization of complicated and expensive and easily disarranged wiring systems and timing and releasing devices. Further objects of the invention are as will appear in the following description.

To avoid these objections to prior devices, this invention provides a system wherein the timed delay in operation of the traflic control devices is abolished. The vehicles themselves in their relative movements determine the signaling and effect their own control without timing. This control is determined by detectingthe presence of a vehicle over an extended area instead of substantially at a point, such extended area having at least a suiiicient sensitivity to the presence of a vehicle at all points throughout its extent,

and being inherently capable of being extended both in length and in width so asto exceed the horizontal area occupied by any vehicle. Such a detector may be arranged to detect the presence of a vehicle within a given area whose width is the lane or lanes used by traffic approaching the intersection and whose length extends away from the intersection to a point suificiently removed therefrom for a vehicle traveling past said point at the greatest speed probable on the highway in question to bring itself to a stop before entering the intersection, this length being in all events greater than a typical single vehicle. This arrangement insures that a vehicle approaching the intersection will either operate the system to display a go or favorable signal, or will receive a stop or unfavorable signal at full stopping distance from the crossing; this stopp distance normally averages 30 feet at 20 miles per hour, 67 feet at 30 miles per hour, and 120 feet at 40 miles per hour. This is in contrast to those vehicle-actuated systems, in which the single-point detectors are frequently placed close to the intersection to minimize difliculties with timed delays, and hence a vehicle has no efiect on the signal until it is much nearer than normal stopping distance.

This extended detecting area may terminate at the margin of the intersection so that a vehicle will not leave its field of influence until it has moved well into the intersection, in plain view from the crossing lane of travel. Beyond this point in the movement of the vehicle there is no necessity of retaining the traiiic signals or other control devices in cleared condition, provided of course there is no other vehicle approaching in either direction on the same route. At once it becomes possible for vehicles on the interfering or crossing way to affect their respective detec-,

tors and obtain a clear signal, without having to wait for a predetermined period of time to elapse, and regardless of the length of time consumed by the first vehicle in passing through the above area.

According to another aspect of my invention a novel form of vehicle detector is contemplated, employing longitudinal members, conducting magnetic flux over a considerable area adjacent to an intersection of traffic lanes, so that the presence of a vehicle within its field will affect the distribution of flux between the longitudinal members in such a manner as to cause an associated electrical circuit to undergo a change. A pulsating or alternating flow of flux may be employed, facilitating the detection of magnetic vehicles or other bodies at rest or moving very slowly, as well as the continuous detection of a body or vehicle moving within the aforesaid field. Suitable reluctance devices may be utilized to produce the desired flux distribution, by separating the longitudinal members from the transverse members and arranging the gaps perpendicularly to the lane of travel or with a covering of magnetic material so that the value of reluctance will not be undesirably decreasedby magnetic bodies improperly or maliciously introduced.

The invention provides a detector having no delicate or moving parts, and which can be completely buried in the roadway, having no exposed or visible portions.

These and other features of the invention as set forth in the appended claims will appear more particularly in the following detailed specification and annexed drawings, in which,-

Fig. l is a schematic wiring diagram of the electrical system of connections used, and an 11- aoeaaaa lustrative embodiment of one arrangement of detectors in relation to the roadways and to the intersection.

Fig. 2 is a top plan view of a single detector arrangement showing its relation with a vehicle approaching an intersection of traffic lanes.

Fig. 3 is a similar view of a modified form of detector.

Fig. 4 is a similar view of another modified form of detector.

Fig. 5 is a similar view of a reluctance device, which may be used to distribute more effectively the magnetic flux in the detector.

Fig. 6 is a view in vertical section taken at right angles to a highway showing a still further form of reluctance device.

Fig. 7 is an end view of the reluctance device shown in Fig. 5.

Fig. 8 is a plan view of a double or duplex"- detector.

A right angle intersection of two highways is illustrated in the drawings, each highway consisting of two lanes of trafiic, although any number of lanes or any number of highways meeting at an intersection in any angular relation could be provided with devices embodying my improved system of control. There are thus shown four intersecting traffic lanes I0, ,I I, I2, and I3, each entering into the intersection which is determined by the projection of the lateral edges of the streets. The corners l5, l6, l1, and I3 are formed by the edges of these streets. The rectangular area defined by connecting the several corners each with its two adjoining corners determines the area of the intersection.

Conventional traflic signals or other right of way indicating devices 20, 2|, 22, and 23, each consisting in the present instance, of red, yellow and green lights, are mounted upon suitable standards for affording control of tramc lanes I2, I 3, l0 and II, respectively. A standard interpretation of the colors is assumed to be, "stop" for red; cauti0n" or warning for yellow; and "go" for green. Electrical return connections for operating the lights are made by grounding one terminal on each of the fixtures. Diagonally opposite standards which control non-interfering lanes following similar routes in opposite directions have their lights connected in parallel: The red, yellow and green lights of signal 20 are connected by wires 25, 26 and 21 to the corresponding lights of signal 22; signal 2! is similarly connected to signal 23 by wires 29, 33 and 3 I.

Free vehicle detectors 3|, 32, 33 and 34 are located under or adjacent to each of the lanes III, II, l2 and i3, respectively. These free vehicle detectors are sensitive to free vehicles, especially as distinguished from a detector which is designed to be sensitive only to vehicles running on a track or similar fixed route or path. Each detector is similarly constructed and operates in the present instance through the magnetic properties of a passing vehicle. Fig. 2 shows more clearly how two elongated members 33 and 31 may be located at either side of the lane of travel 39 which comprises one half the street area between the curbings l0 and 4|. These members should be of high permeability magnetic metal with enlarged terminals 43, ll, 45, and 43 bent toward each other in proper spaced relation. An energizing coil 48 at one end may be connected to a source of alternating current supply and a detector coil 43 at another location may be connected to a suitable relay. Under normal conditions there will be some flux passing through coil apogee:

99 under the action of the energizing coil 99, but upon the entrance oi a vehicle ll between the magnetic members a large part oi this mutual flux will be shunted through the vehicle. The resulting reduction, change, or surge in the current now, through the coil 49 will permit the armature oi the relay to escape from its magnet opposite directions from the pivot point. A resilient spring 33 maintains the arm 59 in a position slightly to one side of the center of movement, and also serves to connect arm 59 to one side of the source of power, herein side 93. Stationary contacts 55 to 19, inclusive, are connected by wires H to 19, inclusive, to the various signal lights.

The armatures of relays 53, 54, 55 and 55 are 4 all grounded and adjustably biased by tension springs of insuiilcient strength to overcome the force of the magnets when energized byAthe normal current induced in the detector coils 49 when no magnetic body is.within the detectors field.- A vehicle entering within the fleld of any de tector causes the respective relay to release its armature, closing contact with its respective associated stationary contact point I9, 89,9l 'or 82. Contact points of oppositely disposed relays are connected by wires 84 and 85. The circuit is completed from'the contacts by wires 81 or 99 to solenoids 99 or 9|, respectively. Movable armatures attracted by these solenoids are pivoted to crank arm 6| or 62 and serve to operate the switch arm 59 to move it over the contacts 65 to 19, inclusive.

Power is supplied through the terminals 92 and connection 95 to all of the apparatus may be employed.

The operation of the system is as follows:- Assume a vehicle enters the lane l3. As it approaches the intersection it comes within the influence of the magnetic field of detector 34, shunting the flux between the parallel members and causing the armature of relay 56 to be released. The contact 82 is grounded, and a circuit is completed from the power supply termiml 93, wire 95, spring 53, arm 59, contact 19, wire 91, contact magnet 9i, wire 98, contact 82 and back through the armature audits ground connection to the other power supply terminal 92. This causes the switch arm 59 to be thrown to the left, and establishes a circuitfrom terminal 93, through wire 95, spring 63, switch arm 59, contact 55, wire II to green lights 2! and 23.

Also, red lights of signals 29 and 22 are illuminated through the. contact 39 and arm 59. A clear road is thus gyepared ahead of the vehicle, and stop signals displayed on both the crossing lanes l9 and I2.

' Switch arm 59 will be retained over contacts 95 and 99 until the vehicle passes entirely out of the field of influence of detector 34 at which time it at once is movable to the caution or opposed position. The detectors may be of ,such length that their field 01' force extends from the border of the intersection to a point on each lane sufflciently removed from the intersection to permit the stopping of any vehicle. This length may be made great enough to accommodate all yehicles traveling at a reasonable speed and should besufllcient to permit the operator to apply his brakes and stop his car before entering the intersection, even though traveling at the highest-s speed permissible along that part of the highway. The switch arm 59 will not be returned by spring 53 until the rear end 01' the vehicle has passed from the field of influence of the detector. The vehicle will by that time have passed well into the intersection in plain view from the crossing lanes. If desired, a simple dash-pot 99 may be connected to the switch arm to render the operation of the arm more even against the action of the spring 63. The dash-pot should not offer suflicient resistance to prevent substantially instantaneous operation of the switch arm when either magnet 9| or 92 is energized.

When the vehicle has passed through, the spring will return thearm 59 to any desired positionaccording to its adjustment. For this purpose difl'erent pins I99, l9i, I92 and I93, all connected to wire 95 are provided, to which the end of the spring may be attached. This permits the use of the system where it is desired to arrange one street as a through-way and the other as an intersecting way. The through-way will normally display a go-signal and the intersecting way a stop-signal, so that those crossing will approach with greater caution. With this arrangement, the two detectors in the through-way may be dispensed with and still achieve largely satisfactory trafllc control. When both highways carry commensurate amounts of traflic the switch arm 59 will be adjusted normally to be returned to a middle position, closing circuit with contacts 81 and 58. These contacts complete thecircuit with all of the yellow or caution lights through wires 12 and I5. While the lever remains in this position a caution signal will be displayed for all lanes of trafllc.

Magnets 99 and 9| are so designed that when the armature of one is slightly withdrawn from its solenoid the tractile force is weakened. This is for two purposes; first to prevent changing of the signals while a vehicle is within' the fleld of a detector and second to prevent the switch arm from locking in a dead center position through the simultaneous approach of two vehicles on intersecting lanes. This last effect is further accentuated by arranging the fixed end of spring 63 in a slightly oiT-center position, and by arranging contacts 11 and 18 to open the circuit to the undesired magnet as soon as the lever is moved by whichever magnet is to act, thus giving a. preference to vehicles approaching the intersection on one street over those on the other. The spring and contacts 11 and 19 may be adjusted to give either street the preference by connecting'the spring to either pins I 9| or I92 and adjusting the contacts correspondingly, through proper movement of the sector on which they are .has passed beyond the field of its detector the effect of the second vehicle on its detector and associated apparatus will cause the signals immediately to shift, allowing it to continue on its way without delay. Since it must acceleratefrom a reduced speed to reach the crossing there is but slight likelihood of interference with the first vehicle even though the first has not passed beyond the intersection. No waste time is therefore required to permit the safe conduct of any number of vehicles over the crossing lanes. Traffic is seldom so heavy on any highway but what there are sufilcient intervals through which a crossing vehicle may pass. A duplex detector, as shown in Fig. 8, having detecting coils d d, at opposite ends and a common energizing coil e in the middle, can be used to lengthen the approach area, to give plenty of time to stop, to provide against the case where extending the side members to get a long detecting area would produce so much normal flux leakage that additional leakage or shunting by a vehicle would be inappreciable. The coils d d are jointly able to pass sufficient current to a mutual relay to hold the latter's armature in open-circuit relation, but while either is affected by a vehicle, the armature closes the circuit as already described.

Another use is that when a vehicle isstanding in the stopped or opposing trafllc lane (as around the corner in Fig. 8) and a second vehicle is in range of d but :1 is empty, this break in the trafiic along the lane of (l -d may be seized upon to permit such standing car in the said opposing lane to control the signals and cross over immediately after the other vehicle leaves d, the signal facing the vehicle in the field of d turning yellow followed by red immediately upon the vacating of d or shortly after as determined by a timer of any known form. The principle governing this phase of the invention is that on a high speed highway, the detector must be long to stop trafllc fairly; but under certain circumstances, a break in traffic of the length of this long detector may rarely occur. Hence the single detector is in effect converted into two, so as to take advantage of a short break to transfer the right of way to the opposing traffic. Manual control may be incorporated into the system with slight obvious and well-known additions to permit use with such extremely heavy traffic, or any other unusual condition as by swinging lever 59 by hand.

Iron or other metal alloy having a high permeability should be used for the elongated magnetic members of the detectors. They may be divided into wires or laminations to reduce eddy current losses. They may also be used to reinforce the concrete employed in the roadway.

The flux may be distributed in any manner that will obtain the desired results. This distribution should be such .as to produce a leakage through a vehicle adjacent the members, substantially proportionate to the flux remaining in the members. Such distribution may be effected by air-gaps having a reluctance of the same order of magnitude as the reluctance encountered by the magnetic flux through the vehicle. An air-gap between terminals 4| and 40, Fig. 2, may control the total magnetic flux in the circuit. A second gap between terminals 43 and 44 should be adjusted to provide a reluctance commensurate with or if possible equal to that offered by the flow of flux through a vehicle or equivalent body between the elongated members. If desired, these gaps may be divided, one-half on each side of the coil, to balance the system more evenly, as in Fig. 3, where two similar elongated members I06 and I06 are shown arranged in proper relation to a curbing IIII. Short magnetic cores I08 and IIII having coils thereon may be introduced between the terminals of these members.

Another form of detector device H2 is shown in Fig. 4, where both coils H3 and H4 are positioned at one end with the ends II and Ill separated. The flux will increase upon the presence of a vehicle I I8 resulting in an increase of current in the relay coil H4 in this type of detector.

The use of a permanently magnetized core 44, III, I34, in conjunction with an electromagnet energized by A. C. can be made to eflect a greater sensitivity to the alternating magnetomotive force in the remainder of the device by raising the average flux density in the iron of the circuit to a point where an alternating magnetomotive force will cause a larger change in flux density than it would if the average flux density were not so raised, because through operating at a point where the slope of the hysteresis curve is steeper the resultant flux is greater.

The reluctance gaps should be shielded or otherwise properly arranged as shown in Figs. 5, 6, and 'l, to prevent changing of their values by the presence of magnetic bodies and the consequent nullification of their action. Terminals I20 and I2I may correspond to any of those described in connection with Figs. 2 or 3. A magnetic shield I23 may surround the path of the leakage flux and prevent it passing through adjacent magnetically permeable bodies. Non-magnetic material I22may be inserted to increase the structural strength. Various other forms might be devised.

It may be advisable to arrange the reluctance aps of the magnetic circuit horizontally to direct the magnetic lines in a perpendicular direction,

thereby preventing disabling the system through the presence of magnetic objects on the surface of a highway above. An end view of a magnetic system under a highway surface I30 is shown in Fig. 6. Longitudinal magnetic members I3I end in terminals I32 having their lower faces directed downwardly. Terminals I33 of another magnetic member I34 are disposed in suitable spaced relation opposing terminals I32. A coil I36 about member I34 serves either as an energizing coil or a relay coil corresponding to those shown in Figs. 2, 3, or 4, as the case may be. The arrangement with gaps below the longitudinal members I II and perpendicular to the highway surface insures a constant value of reluctance without wilful interference from movable objects, since such 0b- J'ects, which could only be applied from above, would shunt flux between members I3I rather than from I3I to I33, shunting and operating rather than rendering the detector inoperative.

The detectors described are sensitive to the presence of both moving and stationary vehicles and extend over a considerable area. They may be buried under the roadway or disposed at the side, provided their field of force projects into the path taken by the vehicles. Their operation differs very considerably from that or detectors which are sensitive at but a single comparatively or a number of abutting detectors may be empioyed ii the area is too large for a single one, or ii traflic conditions so require. Further, having no moving parts in or under the roadway, they are impervious to mud, ice, gravel, and other matter naturally present or improperly introduced. Even the relays may be located outsidethe detector where theyare readily accessible for maintenance.

Detection over an extended area not only eliminates the necessity of timed delay devices which must be set at a maximum time period to take care of trafllc moving at low speeds, producing inflexible time periods and initiating delays and interruptions to traific moving at high speeds. but also permits extending the detector right up to the margin of the intersection so that control over the system by a vehicle is extended to include all movements that are capable of interfering with other trafllc.

While the use of the timed delay principle is not necessary in the ordinary working of the system of the invention, yet its use is contemplated for special purposes, as to guard against tie-up of the signals due to breakdown of a vehicle within the field of influence of a detector, for which contingency two separate relays like 53 can be connected to the same detector in shunt or series, one responding to normal traffic conditions, while the other with a weaker armature spring is designed in effect to ignore the presence of one vehicle and respond only to more than one vehicle within the detector, with the timer, of usual or any known type, arranged to transfer control from the first or normal relay to the emergency one, so that the signals can continue to function in presence of a stalled car, control to revert to the normal relay after removal of the obstructing vehicle. Or the timer may be used where trafiic is so heavy that the paired detectors on a single highway are rarely free of vehicles simultaneously. In these and other special cases, any known form of releasing device may be employed to terminate or revoke the effect of the detectors on this highway after a lapse of a given interval of time, to give the interfering trafiic control of the signals. In this event, it would be desirable to provide some additional device to cause a warning signal to be shown when a signal was about to change from go to stop" in the face of approaching traffic.

The great advantage of the present invention is that the vehicles themselves by their relative time of approach to and of passing through the field of the detector determine the nature and duration of the signal, in direct accord with the fundamental principles of priority of approach to the intersection and relative density of trafllc on the two intersecting ways. Thus, the vehicle first reaching the approach to theintersection sets the signals on its highway to permit traflic thereon to cross, or turn, and sets the signals on the other highway to hold up traffic. If there are vehicles closely following the first, so that at least one remains within the active field of the detector which has set the signal, or the corresponding one across the intersection on the same highway, the signal remains vunchanged until there isabreakinthetramc and theileldsofthese two detectors are momentarily unoccupied. Then, if a vehicle has entered either detector on the other highway, in the meantime, its influence causes the switch to shift and clear the crossing signals before it, only when there is a momentary pause in the transverse trailic. Since the signal stopping the traffic on either highway, is preferably initiated only when the detectors on that highway are free from" vehicles, and the detecting area is of adequate extent back from the intersection to give an approaching vehicle sufllcient time to stop, there is little incentive for a vehicle to crowd in close to its immediate predecessor or rush into the intersection following such vehicle at high speed in order to beat the change of signal, with resulting liability of accident, as com monly accurs with the timed delay systems.

It is apparent that my improved detector could be effectively utilized with a large number of traffic control systems. The system described being advantageous in certain instances, obviously other systems and circuits for control could be employed under special circumstances. For instance, manual control for pedestrian travel could be used, on the order of that already referred to. A hold-over detector could be used within the actual intersection area, as indicated in dotted lines at I9, Fig. 1, to prevent change of signals until a vehicle has left the intersection. It may also readily be seen that with the use of detectors abutting the intersection, a vehicle may make a complete U turn by simply entering into the field of each detector, actuating the signals in succession without stopping, in the absence of the approach of another vehicle. Also, a vehicle not having the right of way may make a right turn though confronted with a red signal, if desired, without having a continuing influence on the signals of the interfering lane. Further additional detectors may be installed for various purposes, as for route selection at irregular or multiple intersections, or a plurality of intercontrolled intersections may be linked together in amanner similar to previous practice.

One of the outstanding features of the inven tion is the use of means extending the detecting area lengthwise of the highway so as to eflect detection over an area instead of at a'point.

While the invention is set forth and described in connection with the employment of energy in the form of magnetic flux, or distributed in accordance with the principles of. the magnetism throughout this detecting area, the use of other forms of energy, including radio frequency electric currents, together with appropriate guiding, conducting, or distributing means of any wellknown character, is also contemplated, operating according to the general principle of a detectable variation or re-distribution effected through the presence or movement of a vehicle at or near any point along the length of such guiding, conducting, or distributing means.

Having thus described particular embodiments of my invention in their preferred forms I do not desire to be limited to the exact form and construction but submit the foregoing for illustrative purposes of the principles involved, rather than in a restricting sense.

What I desire to claim is:-

1. A vehicle detector adapted to control traflic signals, consisting of elongated parallel lengths of magnetically permeable material disposed in parallel relation to a lane of travel throughout a distance longer than the length of the longest typical vehicle, means for producing an alternating magnetic field throughout said magnetic material, and an actuating device operable to work the signals upon the redistribution of the magnetic fiux in the circuit by the positioning of a vehicle within the influence of said field.

2. A detector for lree vehicles having in combination a magnetizing device, a detecting device, and magnetically permeable members extended in the direction of normal travel oi. such vehicles throughout a distance greater than the length of such vehicles, and so disposed that the magnetic flux therein is aifected by the vehicle to be detected, so as to give a detecting impulse to said detecting device.

3. A vehicle detector adapted to control traflic signals consisting of a magnetic circuit adapted to be positioned underground adjacent a trafiic lane for vehicles, longitudinal members included within said circuit of greater length than the vehicles to be detected, means for producing an alternating magnetic field through said circuit and-an actuating device operable to work the signals upon the disturbance of the magnetic circuit by the positioning of a vehicle within the influence of'said field.

4. A vehicle detector for traffic control consisting of a magnetic system adapted to be positioned adjacent a traffic lane for vehicles, magneticmembers included within said system and arranged adjacent the traific lane, means for producing a magnetic field through said members of suitable strength to produce a substantial leakage through a vehicle adjacent said members, a portion of increased reluctance to magnetic flux in said magnetic circuit, said reluctance being approximately equal to the reluctance through said vehicle, means shielding said portion of increased reluctance, and means for detecting thechanged distribution of fiux caused by such leakage so as to indicate at a remote point the presence of such vehicle.

5. A system for regulating traflic having in combination; a detecting device, magnetically permeable members extended in the direction of normal trains of such vehicles throughout a distance greater than the length of such vehicles,

so disposed that the magnetic flux therein is aii'ected by the vehicle to be detected, means for indicating right-ot-way, and means to cause the detecting device to eflect the operation of the indicating means upon said magnetic flux being aflected by a vehicle.

6. Apparatus for directing the operation vehicles having in combination, traflic signals, a magnetic circuit adapted to be positioned underground adjacent a trafiic lane for vehicles, longitudinal members included within said circuit of greater length than the vehicles to be detected, means for producing an alternating magnetic field through said circuit, and devices controlling the action of the signals in response to disturbance oi. the magnetic circuit by the positioning of a vehicle within the influence of said field.

7. In a right-oi-way indicating system, in combination, a signal, a magnetic circuit adapted to be positioned adjacent and apart from a traflic lane for vehicles, magnetic members included within said circuit of greater extent in the direction of travel in such lane than the vehicles to be detected, means for producing an alternating magnetic field through said circuit, and an actuating device operable to work the signal upon the disturbance of the magnetic circuit by the positioning of a vehicle within the infiuence'oi said field.

8. A system for regulating free vehicle traflic where a plurality of lanes of trafiic interfere with one another, including a trafiic control device, a detector having a field of sensitivity covering an area greater than that occupied by any one vehicle and positioned below at least one of the lanes located at the approach to the area of interference, said detector including a magnetizing device, a detecting device, and magnetically permeable members extended in the direction of normal travel of. such vehicles throughout a distance greater than the length of such vehicles, and means controlling the trafiic control device in accordance with the disturbance of the magnetic flux in the magnetically permeable members caused by the presence of a vehicle.

HENRY B. BRAINERD. 

